Aqueous coating compositions

ABSTRACT

PCT No. PCT/GB93/00468 Sec. 371 Date Nov. 3, 1994 Sec. 102(e) Date Nov. 3, 1994 PCT Filed Mar. 5, 1993 PCT Pub. No. WO93/18075 PCT Pub. Date Sep. 16, 1993Aqueous curable polymer dispersion comprising a polyester and/or polyurethane and a polymeric product having a Tg from 25 DEG -100 DEG  C. obtainable by free-radical polymerisation of a mixture of (a) an olefinic monomer free from epoxy and epoxy reactive groups, (b) a monomer and/or oligomer having at least two epoxy groups and (c) a group reactive towards epoxy groups.

This invention relates to crosslinkable aqueous coating dispersions inwhich the basis of the crosslinkability is provided by the reaction inan applied coating between epoxy groups and certain polymer-boundepoxy-reactive groups.

Polymeric film coatings are well established in the technology ofprotection of surfaces, and are frequently required to becomecross-linked for certain applications. Thermal curing (often referred toas storing) is widely used, especially in the case ofmelamine-formaldehyde cured coating systems. However, such systemssuffer the disadvantage of release of formaldehyde on curing. They alsorequire a high storing temperature (typically about 150° C.) which canbe somewhat reduced by use of strong acid catalysts but at the expenseof impairment of the coating performance. Such disadvantages areovercome by the present invention.

Epoxy-cured aqueous coating systems in which epoxy groups andepoxy-reactive groups are present in separate particles of an aqueousdispersion are known from PCT Application No. W091/14715 and U.S. Pat.No. 4,367,298. However, these are expensive to produce and presentdifficulties in the maintenance of storage stability.

When high temperature applications are envisaged for coatingdispersions, as for example in the coating of heated substrates, arelatively high minimum film forming temperature (MFT) for thedispersion can be tolerated, provided that such MFT is the same as, orless than, the temperature of the substrate. This is quite a commonsituation for storing applications on metallic substrates. However, inlow temperature applications, for example room temperature, it isnecessary to depress the MFT of the coating composition, for example bythe addition of a co-solvent (acting as a coalescing solvent). However,care is required in the choice of such MFT depressants. A cosolventwhich partitions strongly in the polymer phase of the aqueous polymerdispersion can itself depress the glass transition temperature (Tg) ofthe polymer in the dispersed particles and which therefore, in certaininstances (notably when the depressed polymer glass transitiontemperature is lower than the storage temperature to which thedispersion is exposed), may lead to premature cross-linking in thepolymer system.

We have discovered that certain water-soluble or water-dispersiblepolymers are particularly effective in suppressing the MFT ofcrosslinkable compositions without significantly affecting the storagestability thereof.

According to the present invention there is provided an aqueous curablepolymer dispersion which comprises a polyester and/or polyurethane and apolymeric product having a Tg within the range 25° C. to 100° C.obtainable or obtained by subjecting to a free-radical-initiatedpolymerisation process a mixture comprising the components:

(a) at least one polymerisable olefinically unsaturated monomer whichdoes not have an epoxy-functional group or an epoxy-reactive group or agroup which is subsequently converted to an epoxy-reactive group;

(b) at least one polymerisable olefinically unsaturated monomer havingat least one epoxy-functional group and/or at least one multi-functionalepoxy compound having an average of 2 or more epoxy groups per moleculeand which is not derived from the polymerisation of an olefinicallyunsaturated monomer system: and

(c) at least one olefinically unsaturated monomer having one or more ofthe following:

(i) at least one carboxyl group such that epoxy-reactive carboxyl groupsare provided directly in the resulting polymeric product and/or suchthat epoxy-reactive amine groups are provided in the resulting polymericproduct by conversion subsequent to polymerisation of at least some ofthe carboxyl groups to epoxy-reactive amine groups;

(ii) at least one hydroxyl group such that epoxy-reactive hydroxylgroups are provided directly in the resulting polymeric product; and

(iii) at least one blocked amine group which is deblocked subsequent topolymersiation to provide epoxy-reactive amine groups in the resultingpolymeric product: and wherein

(d) the level of component (b) based on the sum of components (a), (b),and (c), is from 2 to 48 weight %, preferably from 5 to 30 weight % andmore preferably from 10 to 25 weight %;

(e) the level of component (a) based on the sum of components (a), (b),and (c) is from 50 to 96 weight %, preferably from 60 to 80 weight %;and

(f) the level component (c) based on the sum of components (a), (b), and(c) is from 2 to 40 weight % preferably from 5 to 25 weight %.

The aqueous curable polymer dispersion preferably comprises from 5% to70% by weight (relative to the weight of polymeric product) of thepolyurethane and/or polyester, more preferable 15% to 60%, especially20% to 50% by weight.

The polymeric product preferably has a Tg within the range from 30° C.to 90° C., more preferably 35° C. to 70° C.

The polyesters and polyurethanes are dissolved or dispersed in theaqueous curable polymer dispersion. The polyesters and polyurethanes maybe rendered water-soluble or water-dispersible by arranging for suitableionic and/or non-ionic groups to become incorporated into theirpolymeric structure as a result of using appropriate monomers duringtheir synthesis. Preferred ionic groups are carboxylate and sulphonategroups (made, for example, by neutralising polymer bound carboxyl orsulphonic acid groups) and preferred non-ionic groups includepolyoxyethylene oxide chain-containing groups.

The polyesters may be prepared by methods known per se comprising, forexample, the condensation of appropriate carboxy or sulpho containingmonomers and hydroxy containing monomers.

The polyester may be prepared by polymerisation of polycarboxylic acidand/or their ester forming derivatives and polyols, preferably in thepresence of a catalyst and with the removal of water and/or alcoholformed during the polymerisation.

As examples of polycarboxylic acids and their ester forming derivativesthere may be mentioned C4 to C20 aliphatic, alicyclic and aromatic di-and tri-carboxylic acids (or higher functionality acids) or their esterforming derivatives (such as anhydrides, acid chlorides, and lower alkylesters). Specific examples include adipic acid, fumaric acid, maleicacid, succinic acid, iraconic acid, sebacic acid, nonanedioic acid,decandioic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, terephthalic acid,isophthaiic acid, phthalic acid and tetrahydrophthalic acid. Anhydridesinclude succinic, maleic, phthalic, tetrahydrophthalic acid andhexahydrophthalic and trimellitic anhydrides.

Similarly there are a great number of polyols which may be used inpolyester synthesis for the provision of the hydroxyl component. Thepolyol(s) preferably have from 2 to 6 (especially 2 to 4) hydroxylgroups per molecule. Suitable polyols with two hydroxyl groups permolecule include 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol (neopentylglycol), and diols such as alkoxylated hisphenol A products, e.g.ethoxylated or propoxylated bisphenol A. Dimethylol propionic acid(DMPA) can also be considered as a polyol with two hydroxyl groups permolecule even though it also contains a sterically hindered carboxylgroup. Suitable polyols with three hydroxyl groups per molecule includetriols such as trimethylolpropane (1,1,1-tris(hydroxmethyl)ethane).Suitable polyols with four or more hydroxy groups per molecule includepentaerythritol (2,2-bis(hydroxymethyl)1,3-propanediol) and sorbitol(1,2,3,4,5,6-hexahydroxyhexane).

The polyurethanes containing carboxyl groups may be prepared by reactingorganic polyisocyanate with an organic compound containing at least 2isocyanate reactive groups, e.g. a polyol, preferably in the presence ofa diluent.

The isocyanate terminal prepolymer may be prepared by condensationpolymerisation of an isocyanate and a polyol, for example one of theaforementioned polyols, or a glycol, for example ethylene glycol,propylene glycol, diethylene glycol, neopentyl glycol, 1,4-butanediol,furan dimethanol, cyclohexane dimethanol, glycerol, trimethylolpropane,pentaerythritol and mixtures thereof. The condensation is preferablyperformed in an organic solvent and/or vinyl monomer, followed byneutralisation of any acid groups and dispersion in water.

The preferred isocyanates are aliphatic, cycloaliphatic and aromaticisocyanates. Examples of suitable isocyanates include ethylenediisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate,cyclohexane-1,4-diisocyanate, 4,4-dicyclohexyimethane diisocyanate,p-xylylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-toluenediisocyanate, 2,6-toluene diisocyanate, 4,4-diphenylmethanediisocyanate, 2,4-diphenylmethane diisocyanate, polymethylene polyphenylpolyisocyanates and 1,5-naphthylene diisocyanate. Mixtures ofisocyanates can be used and also isocyanates which have been modified bythe introduction of urethane, allophanate, urea, biuret, carbodiimide,uretonimine or isocyanurate residues.

The polyurethane may be prepared by chain extension of an isocyanateterminal prepolymer using an active hydrogen containing extender, forexample a polyol, an amino alcohol, ammonia, an amine or optionallysubstituted hydrazine.

Examples of suitable polyurethanes include those sold by ZENECA Limitedunder Trade Mark "NEOREZ".

The free radical initiated polymerisation process may be performed byemulsion polymerisation, by suspension polymerisation or by thedispersion in water of a preformed free-radically polymerised polymermade using any polymerisation technique (but usually aqueous emulsionpolymerisation). One such emulsion polymerisation technique iscore/shell (sequential) polymerisation. Emulsion polymerisation ispreferably carried out at temperatures between 30° C. and 95° C. morepreferably between 50° C. and 90° C.

Component (a)

Preferred polymerisable olefinically unsaturated monomers which do nothave epoxy-functional groups or epoxy-reactive groups, or groups whichare subsequently converted to epoxy-reactive groups, comprise certainolefine monomers, vinylidene aromatic monomers, unsaturated carboxylicacid ester monomers, vinyl ester monomers and combinations thereof.

Examples of such monomers include 1,3-butadiene, isoprene, styrene,divinyl benzene, acrylonitrile, methacrylonitrile, vinyl halides such asvinylidene chloride and vinyl chloride, vinyl esters such as vinylacetate, vinyl propionate and vinyl laurate, heterocyclic vinylcompounds, alkyl esters of mono-olefinically unsaturated dicarboxylicacids (such as di-n-butyl maleate and di-n-butyl fumarate) and, inparticular, esters of acrylic acid and methacryiic acid of formula

    CH.sub.2 ═CR.sup.1 COOR.sup.2

where R¹ is H or methyl and R² is alkyl of 1 to 20 carbon atoms (morepreferably 1 to 6 carbon atoms) or cycloalkyl (especially cyclopentyl orcyclohexyl). Examples of esters of acrylic and methacrylic acid includemethyl acrylate, methyl methacrylate, ethyl acrylate, ethylmethacrylate, n-butyl acrylate, n-butyl methacrylate, isopropylacrylate, isopropyl methacrylate, n-propyl acrylate, n-propylmethacrylate, cyclohexyl acrylate and cyclohexyl methacrylate.

In one embodiment component (a) is a polymerisable olefinicallyunsaturated monomer which does not have any epoxy-functional group or anepoxy-reactive group.

Component (b)

The polymerisable olefinically unsaturated monomers having at least oneepoxy-functional group are preferably selected from (i) alphabeta-ethylenically unsaturated acid esters of epoxidised aliphatic andcycloaphatic alcohols, in particular glycidyl acrylate, glycidylmethacrylate, 3,4 -epoxycyclohexyl methyl acrylate and/or cyclohexylmethyl methacrylate and/or (ii) allyl and vinyl esters of epoxidisedaliphatic and cycloaliphatic acids, in particular allyl glycidyl ether,allyl or vinyl 3,4-epoxycyclohexane carboxylate.

The multifunctional epoxy compound having an average of 2 or more epoxygroups is preferably soluble in any of the olefinically unsaturatedmonomers (i.e. in Component (a) and/or (c)) and preferably miscible inthe resulting polymeric product.

The epoxy group(s) of the olefinically unsaturated monomer(s) ofcomponent (b), if present, provide epoxy functionality in the resultingpolymer. Alternatively, or additionally, the epoxy groups of themulti-functional epoxy compound of (b) (not derived from olefinicpolymerisation), if present may also provide epoxy functionality in theresulting aqueous dispersion by becoming incorporated (it is believed)into the polymeric product.

The multifunctional epoxy compounds of component (b) containing anaverage of two or more epoxy groups are, if used, preferably thosederived from: Bisphenol A and epichlorhydrin; "Novalak" resins andepichlorhydrin, for example, trimethylal propane triglycidyl ether.Other useful epoxides are glycidyl ethers or esters of cycloaliphaticepoxides.

Component (c)

The component (c) provides epoxy-reactive functionality in the resultingpolymeric product either directly or indirectly. Direct provision ofepoxy-reactive functionality may be achieved by the use of a carboxyland/or hydroxy group-functional monomer, any carboxyl groups in theresulting polymer being left wholly unconverted to amine groups, or onlya proportion of them being converted to amine groups (carboxyl groupsare of course epoxy-reactive groups in their own right). Indirectprovision of epoxy-reactive functionality may be achieved by using acarboxyl functional and/or amine-blocked functional comonomer andsubsequent to polymerisation effecting conversion of such groups toamine groups. For example, a carboxyl functional monomer can beincorporated into a polymer to give a carboxyl functional polymer andthe resulting carboxyl functional polymer can be reacted with propyleneimine (i.e. iminated) to give an amine functional polymer.Alternatively, a monomer having blocked amine groups can be used, andthese blocked amine groups in the polymer so formed can be subsequentlydeblocked to generate the amine functional polymer.

Preferred olefinically unsaturated monomers having a carboxyl groupinclude (i) alpha beta-unsaturated carboxylic acids, for example acrylicacid, methacrylic acid and iraconic acid (ii) carboxylic acidderivatives of alpha beta-unsaturated esters; addition products ofhydroxyalkyl acrylates and methacrylates to arthydrides, for example, ahexylethyl acrylate additive product with succinic or maleic anhydride:addition products of alpha beta unsaturated acids to lactones; (iii)carboxylic acid derivatives of alpha beta-unsaturated amides, forexample, 3-acrylamido-3-methyl butanoic acid and10-acrylamido-undecanoic acid; (iv) unsaturated aliphatic andcycloaliphatic carboxylic acids.

Preferred olefinically unsaturated monomers having at least one hydroxylfunctional group include (i) alpha beta unsaturated ester derivativescontaining OH groups, for example hydroxymethyl acrylate, hydroxyethylmethacrylate; (ii) carboxylic acid derivatives of alpha beta-unsaturatedamide derivatives containing OH groups, for example, N-hydroxymethylacrylamide; (iii) unsaturated alcohols.

With regard to olefinically unsaturated monomers having a blocked aminegroup which may be de-blocked to give an epoxy-reactive amine group, itis particularly preferred that such amine functionality be introducedinto the dispersion by an imination reaction between an alkylene imineand a polymer having carboxylic acid functional groups, such groups havealready been introduced by using an olefinically unsaturated monomerhaving a carboxyl group when forming .the polymer as described above.The amount of alkylene imine, for example propylene imine, used shouldbe sufficient to iminate the desired proportion of the carboxyl groupsto aminoalkyl ester groups. Preferably the amount used should besufficient to iminate about 5% to 95%, more preferably 20% to 80%, ofthe carboxyl groups in the precursor polymer. The imination techniqueused is well-known in the art, and in this way reactive amine groups canbe formed from carboxyl groups in the dispersion.

In a preferred embodiment component (c) comprises at least one,preferably 1, 2 or 3, olefinically unsaturated monomers having one ormore of the following:

(i) a carboxy group such that epoxy-reactive carboxyl groups areprovided in the resulting polymeric product;

(ii) a hydroxyl group such that epoxy-reactive hydroxyl groups areprovided in the resulting polymeric product; and

(iii) a blocked amine group such that a blocked amine group is providedin the resulting polymer which is capable of being de-blocked (i.e. theblocking group removed) to give an epoxy reactive amine group.

For the purpose of this invention an "aqueous dispersion" means adispersion (e.g. emulsion or suspension) of the polymer in an aqueousmedium of which water is the principle component, sometimes referred toas a latex when the particles are small enough to be colloidallydispersed. Minor amounts of organic liquids, for example organicsolvents may optionally be present.

The level of "total solids" (i.e. total amount of polyester,polyurethane and polymeric product) in the dispersion of the inventionmay be between 10 and 65% by weight of the total weight of thedispersion.

The phrase "at least one" preferably means from 1 to 4, more preferably1 or 2.

It is to be understood that any reference to glass transitiontemperature relates to a polymeric product in which any conversion ofcarboxyl or amine-blocked groups to amine groups has been carried out.

The selected range of Tg for the polymeric product of the inventiondispersion, i.e. the polymer made from polymerisation after any requiredconversion of groups thereon and including the encapsulated epoxycompound if present, can be achieved by appropriate selection of thecomponents used in the polymerisation and their relative proportions.The selected Tg allows excellent storage stability for the resultingaqueous dispersion since the maximum storage temperature to which thedispersion, or a coating formulation made therefrom, is exposed can bechosen so as to be below the Tg of the polymeric product, thusfacilitating (we believe) colloidal stability. It is also possible toensure (by an appropriate choice of epoxy and epoxy-reactive groups)that any selected Tg in this range is below the minimum temperature orwhich curing is likely to occur to any noticeable degree (the effectivecuring temperature), and this (we believe) avoids a significant level ofpremature crosslinking.

Hence the nature of the monomers and epoxy compound employed in thepreparation of the dispersion of the invention and the relativeproportions are such that the defined range of glass transitiontemperature of the polymeric particles in the dispersion ensures (inparticular) that crosslinking does not take place in the dispersion atroom temperature or, for some embodiments, even at relatively highstorage temperatures, for example up to about 50° C. Similarly,colloidal stability of a dispersion latex can be maintained at room orreasonably elevated temperatures. Nevertheless, when a film is formed ona substrate by evaporation of water from a coating dispersion accordingto the invention, or a coating formulation made from it, effectivecross-linking of the polymer chains occurs at the desired curingtemperature which may, depending upon the choice of epoxy groups andepoxy-reactive groups, be usefully lower than the conventional curingtemperature for polymeric storing finishes.

An important feature of the present invention is that highly reactivecombinations of epoxy-functional groups and epoxy-reactive groups can beutilised owing to the fact that, by the choice of the glass transitiontemperature and MFT of the polymer system within the defined range, thepossibility of premature cross-linking in the aqueous latex (orformulations based on the aqueous dispersion) is greatly reduced. Thus,by choosing reactive combinations, curing temperatures as low as 70° C.can be achieved with commercially acceptable rates of cure. Examples ofsuch reactive systems are glycidyl epoxy ester/amine systems. Oneparticularly preferred combination is that in which the epoxy groups arederived from glycidyl methacrylate and the epoxy reactive groups areamine groups derived from imitating polymerised carboxylicacid-containing units as described above.

The aqueous curable polymer dispersion according to the invention maycontain a coalescing solvent, for example a glycol ether, a glycol etheracetate, in particular butoxy ethanol, in addition to the polyesterand/or polyurethane, preferably in a weight percent of 1% to 20%relative to the total weight of polymeric product.

With regard to the polymerisation to form the polymeric product, it ispreferred to add a suitable surfactant to aid emulsification whenemulsion polymerisation is the polymerisation technique employed. Weprefer to use a known anionic and/or a non-ionic surfactant.

The free-radical initiator may be any suitable initiator known in theart, for example ammonium persulphate.

A buffering agent, e.g. sodium bicarbonate, may be used to control thepH during polymerisation.

Various additives commonly used in the formulation of coatingcompositions made from polymer dispersions may be added to thedispersions produced by the process of the present invention. Forexample, plasticisers, levelling agents, de-roamers, thickeners,pigments, fillers, wetting agents, anti-septic and antifungal agents maybe added as necessary to the dispersions described herein.

The invention also provides an aqueous thermally-curable coatingcomposition derived from an aqueous dispersion as hereinbefore defined.

The invention also includes a process for coating a substrate comprisingapplying thereto a dispersion according to the invention, evaporatingwater therefrom and heating the substrate to form a film thereon.

Products of the invention also include a film or cross-linked surfacecoating obtained or obtainable by evaporation of water from and heatingof a dispersion or composition according to the invention and anysubstrate coated with the film or cross-linked surface coating.

Blends of two or more dispersions according to the invention can ofcourse be used for the provision of crosslinked coatings.

The present invention is useful for preparing durable, solvent-resistantand hard surface coatings on many substrates, particularly those ofindustrial and architectural importance requiring curing by theapplication of heat. Thus surfaces (i.e. substrates) such as stone,wood, concrete, brick, ceramic tile and temperature resistant plasticsmay be coated, but the compositions made according to the presentinvention are particularly suited to the coating of various metals.Specific examples of the latter are storing finishes on metallicarticles, for example steel drum linings.

Coating formulations made with the dispersions of the invention providea number of advantages over the conventional compositions for storingfinishes. For example they possess a low MFT, excellent pot-life andlong-term storage properties (i.e. no significant pre-crosslinkingoccurs) even at relatively high storage temperatures, for example up to50° C. The formulations are one-pack systems which make them moreconvenient in use than the majority of prior art formulations which areusually supplied in two-pack form for comparable applications. Thedispersions of the invention are cross-linkable (i.e. curable) attemperatures significantly lower than those required for conventionalstoring finishes, while still producing a durable and hard finish. Alsoa shorter time of heating is generally possible with the formulations ofthe invention to achieve comparable properties of the cured coating.Additionally, the present water-based formulations are safer than thosewhich emit toxic formaldehyde during curing.

The glass transition temperature (Tg) of a polymer system of theinvention dispersion may, if wholly derived from the polymerisation ofolefinically unsaturated monomers (i.e. not including multifunctionalepoxy compound) my be determined empirically by means of the Foxequation. Thus the Tg, in degrees Kelvin, of a copolymer having "n"copolymerised comonomers is given by the weight fractions W of eachcomonomer type and the Tg's of the homopolymers (in degrees Kelvin)derived from each comonomer according to the equation: ##EQU1##

Experimental measurement of Tg may be effected by the use of dynamicmechanical thermal analysis (DMTA) at 1 H_(z), or differential scanningcalorimetry (DSC).

The invention is illustrated by, but not limited to, the followingExamples. All parts, percentages and ratios are expressed on a weightbasis, unless otherwise specified.

General Procedure for Preparation and Testing of Dispersions Exemplified(Including Comparative Dispersions)

All preparations of polymeric products were conducted in a 2 litrereaction vessel equipped with a stirrer, reflux condenser, thermometerand nitrogen purge. A thermostatted water bath was used to heat andreaction vessel. The respective ingredients for the polymerisations wereadded as indicated in the Examples. At the end of the polymerisation alldispersions were adjusted to a pH of 8-9 using 25% aqueous ammoniasolution (unless stated otherwise). Minimum film forming temperatures(MPT) of the dispersions are shown in Table 1. The MFT was measuredafter 30 days storage at 20° C. and at 40° C. for the dispersions. ASheen MFT bar SS3000 was used to measure the MFT. Table 1 also shows theempirical and experimental (DMTA, 1 H_(z) glass transition temperature(Tg) values.

The level of crosslinking was measured using the methyl ethyl ketone(MEK) double-rub technique. The double-rub test assesses the solventresistance of a film and is effected by rubbing the film to and fro witha rag soaked with MEK until the substrate shows through or until 200double rubs have been performed without the substrate showing through(quoted as >200 double rubs). Films of the respective dispersions forthe double rub test were cast on steel panels at room temperature. Thefilms were then stored as indicated in Table 1 and the MEK double rubtest was performed.

EXAMPLE 1

Stage a)--Preparation of polyurethane dispersion

Poly(propylene glycol) 1000 (32.12 g), 1,4-cyclohexane dimethanol (4.16g) and N-methyl-2-pyrrolidone (NMP) were placed in a vessel undernitrogen and stirred to homogenise. The mixture was heated to 40° C. anda solution of toluene diisocyanate (28.04 g) in NMP added over 1 hour,during which the temperature rose to 90° C. A solution of2,2-bis-hydroxymethyl propionic acid (5.68 g) in NMP were added over 1hour at a constant temperature of 60° C. The mixture was cooled to 40°C. and triethylamine (4.5 g) was added to give a prepolymer. The totalamount of NMP used was 30 g.

The prepolymer melt was dispersed in water and chain extended usinghydrazine (2.64 g) and filtered through a cloth of pore size 53 μm togive a polyurethane dispersion having a solids content of 28% and a pHof 9.5.

Stage b)--Preparation of a polymeric product by free-radical initiatedpolymerisation

A monomer mixture (405.33 g) was prepared consisting of Styrene (99.6g), n-butylmethacrylate (148.8 g), n-butyl acrylate (31.6 g), glycidylmethacrylate (100 g), β-carboxyethyl methacrylate (20 g) and surfactant(Aerosol OT 75, 5.33 g).

40.53 g of the monomer mixture was added to a mixture of water (589.37g), surfactant (Nansa AS40, 2.1 g), sodium hydrogen carbonate (1.2 g)and ammonium persulphate initiator (2.0 g) under nitrogen at 45° C. Themixture was heated to 85° C.±2° C. and the onset of polymerisation wasmarked by an exotherm of ca 3°-5° C.

The remaining monomer mixture (364.8 g) was added over 11/2 hour,maintaining the temperature at 85° C.±2° C., and the mixture stirred fora further 1/2 hour after the addition was complete. The resultantproduct was filtered through a gauze of pore size 53 μm to give apolymeric product having a solids content of 40% and pH of 4.5. The pHwas finally adjusted to pH 8 using 25% ammonia solution.

Stage c)--Preparation of the aqueous curable polymer dispersion

The polyurethane dispersion prepared as in Stage a) (122 g, 30 parts)was added to a stirred polymeric product prepared as in Stage b) (200 g,70 parts) over 5 minutes. After 15 minutes stirring the resultantmixture was filtered through a gauze of pore size 53 μm to give anaqueous curable polymer dispersion having a solids content of 35.5% anda pH of 8.

EXAMPLE 2

Stage a)--Preparation of a polymeric product by free-radical initiatedpolymerisation

A monomer mixture (400 g) was prepared consisting of Styfete (120 g),n-butylmethacrylate (112 g), 2-ethylhexylacrylate (40 g), glycidylmethacrylate (100 g), methacrylic acid (14 g) and acrylic acid (14 g).

40 g of the monomer mixture was added to a mixture of water (466.5 g),surfactant (Nansa AS40, 3.16 g) and ammonium persulphate initiator (2.0g) under nitrogen at 45° C. The mixture was heated to 80° C.±2° C. andthe onset of polymerisation was marked by an exotherm of ca 5° C.

The remaining monomer mixture (360 g) was added over 11/2 hour,maintaining the temperature at 85° C.±2° C., and the mixture stirred fora further 1/2 hour after the addition was complete. 5 minutes after theaddition of remaining monomer mixture began a solution of a surfactant(Nansa AS40, 7.89 g) in water (120 g) was also added over a period of 80minutes. The resultant product was filtered through a gauze of pore size53 μm to give a polymeric product having a solids content of 40%. The pHwas finally adjusted to pH 8 using 25% ammonia solution.

Stage b)--Preparation of an aqueous curable polymer dispersion

A polyurethane dispersion (NEOKEZ R972, available from ZENECA Limited,50 parts) was added to the stirred polymeric product of Stage a) (50parts) over 5 minutes. After 15 minutes stirring the resultant mixturewas filtered through a gauze of pore size 53 μm to give an aqueouscurable polymer dispersion having a solids content of 36.5% and a pH of8.

EXAMPLE 3

The method of Example 2 stages a) and b) were repeated except that inplace of NEOREZ R972 there was used NEOREZ K981 as polyurethane.

The resultant aqueous curable polymer dispersion had a solids content of35.5% and a pH of 8.2.

EXAMPLE 4

Stage a)--Preparation of polymeric product having amine groups

A sample of a polymeric product (200 g) was prepared as described inExample 2, Stage a) except that the pH was adjusted to pH 6.5. Theproduct was warmed to 33° C. and propyleneimine (2.9 g) added over 45minutes. After stirring for 2 hours the mixture was cooled to 20° C. andfiltered through a gauze of pore size 53 μm to give a polymeric productof pH 10, having a solids content of 42%.

Stage b)--Preparation of aqueous curable polymer dispersion

A polyurethane dispersion prepared as described in Example 1, Stage a)(50 parts) was added to a stirred polymeric product prepared asdescribed in Example 4, Stage a) (50 parts) over 5 minutes. After 15minutes stirring the resultant mixture was filtered through a gauze ofpore size 53 μm to give an aqueous curable polymer dispersion having asolids content of 34% and a pH of 8.5.

EXAMPLE 5

The method of Example 1, Stage c), was repeated except that in place ofthe polymeric product from Stage b) (70 parts) there was used thepolymeric product from Example 2, Stage a) (70 parts).

The resultant aqueous curable polymer dispersion had a solids content of35.5% and a pH of 8.

                                      TABLE 1                                     __________________________________________________________________________              Glass transition temperature  MEK Double Rubs                                 (Tg °C.)                                                                             MFT (°C.)                                                                              120° C., 30 minutes cure                        Experimental                                                                         Stored at 20° C.                                                               Stored at 40° C.                                                                      Stored at 40° C.        Film from Empirical                                                                            DMTA, 1 Hz                                                                           for 30 days                                                                           for 30 days                                                                           As prepared                                                                          for 30 days                    __________________________________________________________________________    Example 1, Stage b)                                                                     50     54     52      --      >200   >200                           (PU absent)                                                                   Example 1, Stage c)                                                                     --     --     less than 5                                                                           less than 5                                                                           >200   >200                           (PU present)                                                                  Example 2, Stage a)                                                                     50     52     50      --      >200   --                             (PU absent)                                                                   Example 2, Stage b)                                                                     --     --     less than 5                                                                           less than 5                                                                           >200   >200                           (PU present)                                                                  Example 3 --     --     less than 5                                                                           less than 5                                                                           >200   >200                           (PU present)                                                                  Example 4, Stage a)                                                                     50     55     53      --      >200   --                             (PU absent)                                                                   Example 4, Stage b)                                                                     --     --     less than 5                                                                           less than 5                                                                           >200   >200                           (PU present)                                                                  Example 5 --     --     less than 5                                                                           less than 5                                                                           >200   >200                           (PU present)                                                                  __________________________________________________________________________     "PU" means polyuretane                                                   

EXAMPLES 6 AND 7

Stowed enamel finishes were prepared by formulating the aqueous curablepolymer dispersions from Example 1, Stage c) or Example 5 as follows togive present Examples 6 and 7 respectively:

    ______________________________________                                        Premix                                                                        (1)  Water                     1.41   g                                       (2)  Drewplus 4201             0.08   g                                       (3)  Disperse AYD W22          0.22   g                                       (4)  `Borchigel` L75           0.30   g                                       (5)  Butoxyethanol             1.40   g                                       (6)  `Surfynol` 104H           0.30   g                                       (7)  Amp 90                    0.33   g                                       (8)  Sodium Nitrite (30%)      0.47   g                                       Pigments                                                                      (9)  Kronos 2190               25.60  g                                       Let Down                                                                      (10) Aqueous curable polymer dispersion from                                                                 69.89  g                                            Example 1, Stage c) or Example 5                                         ______________________________________                                         PVC = 17.69                                                              

Method

To water ((1), 1.41 g) was added (10) (34.99 g) followed by (2), (3),(4), (6) and (7). The mixture was stirred slowly and (8) and (9) wereadded, the mixture stirred well, and (5) was added. The mixture wasdispersed at high speed and the reminder of 10 (34.99 g) added. Themixture was passed through a bead mill and applied to steel panels usinga K-bar (100 μm wet film thickness) and cured by heating to 120° C. for1/2 hour. The resultant stowed enamel finishes were found to posses theproperties shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________             MEK          Surface Hardness                                                                       Conical Mandril                                Example Number                                                                         Double Rubs                                                                          Petrol Soak                                                                         Konig Sec.                                                                             Flexibility                                    __________________________________________________________________________    6        >200   Pass  130      Pass                                           7        >200   Pass  150      Pass                                           __________________________________________________________________________     *Cure conditions 120° C., 30 minutes.                             

We claim:
 1. An aqueous curable polymer dispersion which comprises apolyester and/or polyurethane and polymeric product having a Tg withinthe range 25° C. to 100° C. obtainable by subjecting to afree-radical-initiated polymerisation process a mixture comprising thecomponents(a) at least one polymerisable olefinically unsaturatedmonomer which does not have an epoxy-functional group or anepoxy-reactive group or a group which is subsequently converted to anepoxy-reactive group; (b) at least one polymerisable olefinicallyunsaturated monomer having at least one epoxy-functional group and/or atleast one multi-functional epoxy compound having an average of 2 or moreepoxy groups per molecule and which is not derived from thepolymerisation of an olefinically unsaturated monomer system: and (c) atleast one olefinically unsaturated monomer having one or more of thefollowing:(i) at least one carboxyl group such that epoxy-reactive aminegroups are provided in the resulting polymeric product by conversionsubsequent to polymerisation of at least some of the carboxyl groups toepoxy-reactive amine groups; (ii) at least one hydroxyl group such thatepoxy-reactive hydroxyl groups are provided directly in the resultingpolymeric product; and (iii) at least one blocked amine group which isdeblocked subsequent to polymerisation to provide epoxy-reactive aminegroups in the resulting polymeric product and wherein: (d) the level ofcomponent (b) based on the sum of components (a), (b), and (c), is from2 to 48 weight %; (e) the level of component (a) based on the sum ofcomponents (a), (b) and (c) is from 50 to 96 weight %; and (f) the levelof component (c) based on the sum of components (a), (b) and (c) is from2 to 40 weight %.
 2. An aqueous curable polymer dispersion according toclaim 1 wherein component (a) is 1,3-butadiene, isoprene, styfete,divinyl benzene, acrylonitrile, methacrylonitrile, a vinyl halide, avinyl ester, a heterocyclic vinyl compound or an alkyl ester of amono-olefinically unsaturated dicarboxytic acid.
 3. An aqueous curablepolymer dispersion according to claim 1 wherein component (a) is offormula

    CH.sub.2 ═CR.sup.1 COOR.sup.2

where R¹ is H or methyl and R² is alkyl of 1 to 20 carbon atoms orcycloalkyl.
 4. An aqueous curable polymer according to any one of claims1 to 3 wherein Component (c) comprises at least one olefinicallyunsaturated monomer having one or more of the following:(i) a hydroxylgroup such that epoxy-reactive hydroxyl groups are provided in theresulting polymeric product; and (ii) a blocked amine group such that ablocked amine group is provided in the resulting polymer which iscapable of being de-blocked (i.e. the blocking group removed) to give anepoxy reactive amine group.
 5. An aqueous curable polymer dispersionaccording to any one of the preceding claims wherein themulti-functional epoxy compound is soluble in component (a) and/or (c).6. An aqueous curable polymer dispersion according to and one of thepreceding claims which contains a coalescing solvent.
 7. An aqueouscurable polymer dispersion according to claim 1 wherein the polyurethaneand polyester contain carboxylate or sulphonate groups.
 8. An aqueouscurable polymer dispersion according to any one of claims 1 to 7 whereinthe mixture comprising components (a), (b) and (c) contains asurfactant.
 9. An aqueous curable polymer dispersion according to claim1 wherein the components (a), (b) and (c) are respectively asfollows:Component (a) comprises 1,3-butadiene, isoprene, styrent,divinyl benzene, acrylonitrile, methacrylonitrile, a vinyl halide, avinyl ester or an ester of acrylic acid or methacrylic acid of theformula:

    CH.sub.2 ═CR.sup.1 COOR.sup.2

where R¹ is H or methyl and R² is alkyl of 1 to 20 carbon atoms orcycloalkyl; Component (b) comprises glycidyl acrylate, glycidylmethacrylate, 3,4-epoxy cyclohexylmethylacrylate, cyclohexylmethylacrylate, allyl glycidyl ether or allyl or vinyl3,4-epoxycyclohexane carboxylate. Component (c) comprises anolefinically unsaturated monomer having one or more of the following(i)a hydroxyl group such that epoxy-reactive hydroxyl groups are providedin the resulting polymeric product; and (ii) a blocked amine group suchthan a blocked amine group is provided in the resulting polymer which iscapable of being de-blocked (i.e. the blocking group removed) to give anepoxy reactive amine group.
 10. A process for coating a stone, wood,concrete, brick, ceramic tile or temperature resistant plastic substratecomprising applying thereto an aqueous curable polymer dispersion,evaporating water therefrom and heating the substrate to form a filmthereon; wherein the dispersion comprises a polyester and/orpolyurethane and polymeric product having a Tg within the range 25° C.to 100° C. obtainable by subjecting to a free-radical-initiatedpolymerisation process a mixture comprising the components:(a) at leastone polymerisable olefinically unsaturated monomer which does not havean epoxy-functional group or an epoxy-reactive group or a group which issubsequently converted to an epoxy-reactive group; (b) at least onepolymerisable olefinically unsaturated monomer having at least oneepoxy-functional group and/or at least one multi-functional epoxycompound having an average of 2 or more epoxy groups per molecule andwhich is not derived from the polymerisation of an olefinicallyunsaturated monomer system; and (c) at least one olefinicallyunsaturated monomer having one or more of the following:(i) at least onecarboxyl group such that epoxy-reactive carboxyl groups are provideddirectly in the resulting polymeric product and/or such thatepoxy-reactive amine groups are provided in the resulting polymericproduct by conversion subsequent to polymerisation of at least some ofthe carboxyl groups to epoxy-reactive amine groups; (ii) at least onehydroxyl group such that epoxy-reactive hydroxyl groups are provideddirectly in the resulting polymeric product; and (iii) at least oneblocked amine group which is deblocked subsequent to polymerisation toprovide epoxy-reactive amine groups in the resulting polymeric productand wherein: (d) the level of component (b) based on the sum ofcomponents (a), (b), and (c), is from 2 to 48 weight %; (e) the level ofcomponent (a) based on the sum of components (a), (b) and (c) is from 50to 96 weight %; and (f) the level of component (c) based on the sum ofcomponents (a), (b) and (c) is from 2 to 40 weight %.
 11. A filmobtained by evaporation of water from and heating of a dispersionaccording to claim
 1. 12. An aqueous curable polymer dispersionaccording to claim 1 which comprises a polyurethane and a polymericproduct having a Tg within the range 25° C. to 100° C. obtainable bysubjecting to a free-radical-initiated polymerization process, a mixturecomprising:(a) an alkyl acrylate or methacrylate; (b) glycidyl acrylateor methacrylate; and (c) acrylic or methacrylic acid.
 13. A dispersionaccording to claim 12 wherein (a) is n-butyl methacrylate; (b) isglycidyl methacrylate; and (c) is acrylic acid.
 14. A process accordingto claim 10 wherein the substrate is concrete.
 15. A process for coatinga substrate comprising applying thereto an aqueous curable polymerdispersion and evaporating water therefrom and heating the substrate toform a film thereon, wherein the dispersion comprises a polyester and/orpolyurethane and polymeric product having a Tg within the range 35° C.to 70° C. obtainable by subjecting to a free-radical-initiatedpolymerisation process a mixture comprising the components.(a) at leastone polymerisable olefinically unsaturated monomer which does not havean epoxy-functional group or an epoxy-reactive group or a group which issubsequently converted to an epoxy-reactive group; (b) at least onepolymerisable olefinically unsaturated monomer having at least oneepoxy-functional group and/or at least one multi-functional epoxycompound having an average of 2 or more epoxy groups per molecule andwhich is not derived from the polymerisation of an olefinicallyunsaturated monomer system; and (c) at least one olefinicallyunsaturated monomer having one or more of the following:(i) at least onecarboxyl group such that epoxy-reactive carboxyl groups are provideddirectly in the resulting polymeric product and/or such thatepoxy-reactive amine groups are provided in the resulting polymericproduct by conversion subsequent to polymerisation of at least some ofthe carboxyl groups to epoxy-reactive amine groups; (ii) at least onehydroxyl group such that epoxy-reactive hydroxyl groups are provideddirectly in the resulting polymeric product; and (iii) at least oneblocked amine group which is deblocked subsequent to polymerisation toprovide epoxy-reactive amine groups in the resulting polymeric productand wherein: (d) the level of component (b) based on the sum ofcomponents (a), (b), and (c), is from 2 to 48 weight %; (e) the level ofcomponent (a) based on the sum of components (a), (b) and (c) is from 50to 96 weight %; and (f) the level of component (c) based on the sum ofcomponents (a), (b) and (c)is from 2 to 40 weight %.
 16. A processaccording to claim 15 wherein component (a) is 1,3-butadiene, isoprene,styrene, divinyl benzene, acrylonitrile, methacrylonitrile, a vinylhalide, a vinyl ester, a heterocyclic vinyl compound or an alkyl esterof a mono-olefinically unsaturated dicarboxylic acid.
 17. A processaccording to claim 15 wherein component (a) is of formula

    CH.sub.2 ═CR.sup.1 COOR.sup.2

where R¹ H or methyl and R² is alkyl of 1 to 20 carbon atoms ofcycloalkyl.
 18. A process according to claim 15 wherein Component (c)comprises at least one olefinically unsaturated monomer having one ormore of the following:(i) a carboxy group such that epoxy-reactivecarboxyl groups are provided in the resulting polymeric product; (ii) ahydroxyl group such that epoxy-reactive hydroxyl groups are provided inthe resulting polymeric product; and (iii) a blocked amine group suchthat a blocked amine group is provided in the resulting polymer which iscapable of being de-blocked (i.e. the blocking group removed) to give anepoxy reactive amine group.
 19. A process according to claim 10 or 15wherein the components (a), (b) and (c) are respectively asfollows:Component (a) comprises 1,3-butadiene, isoprene, styrene,divinyl benzene, acrylonitrile, methacrylonitrile, a vinyl halide, avinyl ester or an ester of acrylic acid or methacrylic acid of theformula:

    CH.sub.2 ═CR.sup.1 OOR.sup.2

where R¹ is H or methyl and R² is alkyl of 1 to 20 carbon atoms orcycloalkyl; Component (b) comprises glycidyl acrylate, glycidylmethacrylate, 3,4-epoxy cyclohexylmethylacrylate, cyclohexylmethylacrylate, allyl glycidyl ether or allyl or vinyl3,4-epoxycyclohexane carboxylate. Component (c) comprises anolefinically unsaturated monomer having one or more of the following(i)a carboxy group such that epoxy-reactive carboxyl groups are provided inthe resulting polymeric product; (ii) a hydroxyl group such thatepoxy-reactive hydroxyl groups are provided in the resulting polymericproduct; and (iii) a blocked amine group such that a blocked amine groupis provided in the resulting polymer which is capable of being deblocked(i.e. the blocking group removed) to give an epoxy reactive amine group.20. A process according to claim 15 wherein the substrate is a metal.21. A process according to claim 20 wherein the substrate is a steeldrum.
 22. A process for coating a substrate comprising applying theretoa dispersion as defined in claim 15, evaporating water therefrom andheating the substrate to form a film thereon.